BY MOLECULAR COALESCENCE. 105 
the surface of the oyster, to receive the carbonate of lime 
precipitated from the water, which has free access to the 
surface of this membrane next the shell. In consequence 
of this membrane, with the calcareous matter formed upon 
it, beginning to adhere, first to the middle part of the 
previously formed layer of shell, and last to the circum- 
ferential parts, the water in which the oyster is placed 
can easily pass under those parts of this layer which are 
being calcified. And also in this way the water is gra- 
dually shut out from the parts of this layer as their calcifi- 
cation becomes completed. As the form of the growing 
oyster becomes less convex, its surface does not keep 
parallel with that of the shell; hence, the membrane 
formed on this surface bridges over the most concave part 
of the shell, and a space is left, at first between the shell 
and this membrane, but afterwards, when the membrane 
is calcified, this space is of course between the last two 
layers of shell. It is thus that these interlaminar cavities 
are formed. ‘These are the portions of membrane, which, 
when only partially calcified, have been already noticed as 
displaying the most perfect forms of the globular car- 
bonate of lime. (See fig. 6,'4, which is a representa- 
tion of the shell of one of the largest kinds of oysters ; 
a, a, marking interlaminar spaces in which the alkaline 
fluid was contained; 6, 6, similarly formed spaces, but 
without fluid, and filled up with amorphous carbonate of 
lime ; ¢c, c, septa between the spaces containing the fluid 
before mentioned. B is a representation of portions of 
calcifying membrane, taken from the part where this 
membrane bridges over the deepest parts of the shell, as 
represented by c¢, fig. A; a, a, marking the molecular 
state ; b, b, single spherules and dumb-bell-shaped particles ; 
c, laminated globules, in which the cross can be seen by 
